Pregnant mice who exercise are more likely to deliver offspring with no serious heart defects, a new study has found.

Researchers at Washington University School of Medicine in St. Louis, Mo., put running wheels in the cages of old and young mice that were genetically likely to deliver offspring with heart problems. Some were allowed to exercise before becoming pregnant and others were sedentary to act as a control group.

The older, exercised mothers gave birth to far fewer mice with heart problems compared to the older sedentary mice.

More than 20% of the sedentary mice delivered pups with heart defects.

"Most remarkably, voluntary exercise, whether begun by mothers at a young age or later in life, can mitigate the risk when they are older. Thus, even when the offspring carry a causal mutation, an intervention aimed at the mother can meaningfully reduce their risk of congenital heart disease," the study says.

What this could mean for humans remains to be seen, but the Society of Obstetricians and Gynaecologists of Canada recommends pregnant women without complications do regular aerobic and strength-conditioning workouts.